Maybe you constantly miss those two kanjis because you haven’t really learned the little difference between them?
Maybe the meaning of those different kanjis is confusing you and adding a less ambiguous synonym could help?
Maybe your problem with this kanji is that it’s short enough to type semi automatically, but tricky enough that you misspell it even tho you know the answer?

I would love an addon that take your leech list and figures out why you are failing them, because sometimes the reason isn’t obvious.

Even identifying which kanji have a tendency to get higher fail rates or are more likely to drop from enlightened would give you enough info to A/B test whether the issue is lookalikes, mnemonics, etc.

I’d assume that Koichi and co had tested (or analysed) retention/progression rates after they changed timings from 15mins to 1hr intervals, for example, and from 3 day to 2 day SRS for apprentice -> guru.